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Econowave Speakers 


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build, hack, tweak, share, discover, J 

Econowave Speakers 

Written By: Ross Hershberger 


Adjustable wrench (1) 

Chisel (1) 

or scraper, or putty knife 

Drill (1) 

Dust mask (1) 

Gloves (1) 

Jigsaw (1) 
or coping saw 

Needlenose pliers (1) 

Plastic bag (1) 

Sandpaper (1) 

Screwdrivers (1) 

Sharpie marker (1) 

Soldering iron (1) 

Utility knife (1) 

Wire cutter (1) 


Advent Loudspeakers (2) 
or similar; 6"x6" is plenty 

Constant radiation horns (2) 
aka waveguides; $13 

Band- Aids (1) 

Horn driver (2) 

aka compression drivers: $41 

ZilchLab EconoWave crossover PCBs 

from ZilchLab, i am zilch(S> bare 
board for $20 or fully assembled for 
additional cost. Or you can wire the 
crossover circuits on plain breadboard. 

L-pad volume controls (2) 

Resistor (2) 

Capacitor (2) 

Inductor coils (2 of each) 

Painter's tape (1) 

Speaker wire (9') 

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Econowave Speakers 

Plywood (2) 

Plastic tubing (1) 

for screw spacers. You can use the 

barrel of a stick ball -point pen. 

Binding post (2 pair) 
aka speaker terminals 

Speaker gasketing tape (1 roll) 

Sheet metal screws (20) 

Wood screws (8) 

Refoaming kit (1) 

optional: if the foam is decayed around 
your original woofers. I recommend the 
kits from Rick Cobb, 
rcobb(3)tampabay . rr. com. 


Last year on the Audiokarma ( ) discussion boards, members 
Zilch and Jackgiff shared a project that rocked the online audiophile community. They 
designed a treble waveguide and crossover system that greatly improves the sound from 
older speakers with "fried egg" style tweeters. 

Waveguides are horns that disperse high-frequency sounds evenly over a wide area, rather 
than letting them fall off at the sides. This gives the speakers "constant directivity," which 
means they sound more natural to listeners who aren't in the center sweet spot, between 
and in front of the speakers. 

Zilch and Jackgiff also designed a replacement crossover circuit that balances the sound 
across the new combination's optimal 1,600Hz crossover point, routing low frequencies to 
the speaker's great original woofers and high frequencies to the new compression drivers. 
Zilch sells PCBs for building this crossover. 

I tried the conversion myself on some 1970s-era Advent Large speakers. It cost a couple 
hundred dollars, but the results were outstanding: the modified old Advents performed like 
thrillingly clear, state-of-the-art speakers that audiophiles pay thousands for. Since then, I've 

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Econowave Speakers 

built and sold a second pair, and many other Audiokarma members have built multiple pairs 
of these speakers. 

• Pull off the speaker grilles and then wrench off the grille attachment blocks that are stapled 
and glued to the baffle. Unscrew and pull out the woofer and tweeter, cutting their wires. 
Pry off the plastic trim. 

• Wearing a dust mask and gloves, pull out the fiberglass batting and set it aside in a closed 

• Pull out the staples and chisel off the glue inside to remove the original crossover circuit. 
Sand off any glue residue. Repair and refinish the cabinet as desired. 

• Tip: Never use steel wool on a loudspeaker; it sheds steel particles that clog the 
driver's magnet gap. 

• Note: On old speakers, the foam around the woofers may have cracked and 
disintegrated. This compromises the air seal essential to the bass performance and 
makes the woofer rattle and sound bad. Fortunately, it's 100% repairable. You can use a 
kit to replace the foam surround yourself (see Parts list), or take them to a repair shop; I 
ike Audio Atlanta ( ). 

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Econowave Speakers 


• In each speaker baffle, cut a 
10 1 /2 n x5" clearance hole for the new 
waveguide, aligning the top edge 
with the existing tweeter hole. I 
taped off the area, drew cut lines, 
and used a jigsaw with a 3" blade. 

• Tape over the cabinet rim and hold 
the jigsaw above it to avoid 
scratching it. Drop the waveguide 


Mark and drill the ten 1/16" 
mounting holes. 

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Econowave Speakers 

• Assemble a crossover circuit for 
each speaker, referring to the 
schematic. It's easiest to build 
them on the printed circuit boards 
from ZilchLab, which come with 
instructions, but the circuit is 
simple enough to wire together 
neatly on plain breadboard. 

• Solder three 8" single wires running 
offboard for the L-pad tweeter 
volume control. The L-pad uses 2 
potentiometers, a series and a 
shunt, to let you adjust the 
tweeter's volume without changing 
its overall impedance. 

• Also solder two 24" 2-conductor 
speaker wires for the woofer and 
tweeter, and mark the positive (+) 
lead on both. 

• Crimp the slide-on connectors 
provided with the compression 
driver onto the tweeter leads. 

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Econowave Speakers 

Note: The crossover circuit, L-pad, and speaker terminals are mounted to a 5"x5" square 
of plywood inside the cabinet. 

Drill a 3/8" hole through the plywood for the L-pad knob shaft, and 9/32" holes spaced 3/4" 
apart for the speaker posts, close enough to the L-pad so they'll all fit through the cabinet's 
original terminal hole in back. Also drill a 1/8" hole at each corner of the plywood panel, for 
mounting it. 

Solder the L-pad wires to the L-pad terminals, following the schematic and labels 1, 2, and 
3 on the board. Rim the cabinet's terminal hole with foam gasketing tape, and then mount 
the plywood panel to the speaker with screws. 

Position the crossover board on the inside of the panel, and screw on the knob and posts 
on the other side, using washers if necessary. Secure the crossover board over the 
speaker terminal shafts using the supplied nuts. 

Finally, screw down the free edge of the crossover board, opposite the terminal shafts, 
with #6x3/4" wood screws and plastic-tubing spacers cut to size. 

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Econowave Speakers 

• Pull the speaker leads through their baffle holes, leaving plenty of slack inside, and tape 
them to the edge of the cabinet. Carefully replace the fiberglass batting, loading it evenly. 
Replace the cheesecloth behind the woofer hole, and rim the woofer and waveguide holes 
with more foam gasketing tape. 

• Screw the compression driver to the waveguide, connect the tweeter leads, and mount the 
waveguide to the baffle with ten #6x5/8" sheet metal screws and #6 washers. 

• The waveguide fits the Utility model without trimming, but the other speaker models require 
some more work. With the Original Large Advent, sand 1/16" (or less) from both sides of 
the waveguide to make it fit. The New Large Advent has a bit less space, so you can trim 

1/4" off each edge of the waveguide, or get tricky with a router and undercut the walnut 
rim to make room to slide the waveguide edge underneath. I've seen both done, and I'd 
just cut away the plastic waveguide edge myself, rather than attempting fancy router work. 

• To reinstall the plastic trim, shave it down where necessary to clear the waveguide rim on 
each side. Nail in the top, bottom, and one side piece using 1/4" brads, and screw in the 
other side so it can be removed for service. 

• Solder the woofer wires to their terminals, observing polarity. Screw the woofer down and 
replace the grille. That's it! 

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Econowave Speakers 

• Here are some additional 
restoration options, mostly 
cosmetic, that won't affect the 
speakers' sound: 

• For a homogenous appearance, 
paint the cabinet back, woofer 
frame, baffle, and screws all 
black. You'll need 1/2 pint of 
interior latex trim paint. 

• To mount the woofers more 
securely, drill out their screw 
holes to 7/32" and press in eight 
8-32 T-nuts. 

• Make new grilles using the Large 
Corner Grill Frame Kit and an 
extra set of corners (Parts 
Express #260-344 and #260- 
345). Choose thin, stretchy 
fabric, like polyester jersey 
fabric (1yd). Attach the grille 
with velcro tape, and the fabric 
with foam tape. 

This project first appeared in MAKE Volume 20, page 150. 

This document was last generated on 201 2-1 1 -03 03:30:50 AM. 

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